Around the world, public health organizations at all levels of government and the partners that support them are responding to pandemic influenza. Infectious disease experts predicted a pandemic, saying it was not a question of if but when. They were right. Drawing on recent experiences with Severe Acute Respiratory Syndrome (SARS) and concerns over avian influenza (H5N1), the World Health Organization (WHO) and other health authorities urged nations and local governments to prepare pandemic influenza response plans. Many Ministries Of hHalth (MOH) and subnational Departments Of Health (DOH) around the world have activated those plans and are sharing data as required by the updated International Health Regulations (IHR).